Contoured clamshell container

ABSTRACT

A clamshell container comprising a tray and a cover formed from a blank; the tray including a bottom and four curved side walls foldable upward from the four edges of the bottom along arcuate fold lines, the tray walls having defined corners inwardly offset relative to the center points of the walls; and a cover provided with corresponding walls, at least three of which are folded from arcuate fold lines along corresponding edges of a cover top panel and which define depending arcuate cover walls and a cover with a maximum width at transverse centerlines between opposed sets of walls and minimum widths at corners defined by the cover walls; the cover pivotally closing over the tray with the arced walls of the tray received within the arced walls of the cover and engaging therewith.

CLAIM OF PRIORITY UNDER 35 U.S.C. §119(e)

Applicant claims the benefit of priority of Provisional Patent Application No. 60/857,801, filed on Nov. 9, 2006.

BACKGROUND OF THE INVENTION

Clamshell containers of paperboard and like sheet materials have long been known and used as takeout cartons for foodstuffs, particularly although not exclusively in fast food establishments. As will be recognized, such containers are, for the most part, of a square configuration intended to generally conform to and principally package hamburgers and other foodstuffs of similar shapes.

Because of the planar nature of the paperboard panels which fold from a blank to define the container, and as the typical hamburger is round, the conventional clamshell container includes rather large defined interior air spaces about a received hamburger, particularly at the corners of the container. Such air spaces have been found to be a substantial source of heat loss from any warmed or heated foodstuff. Likewise, the lack of an effective seal between the lid and tray of the conventional paperboard clamshell container can also be a potential source of substantial heat loss. However, little attention has heretofore been directed to addressing the heat loss problem in such containers.

Another factor to be considered in the formation of paperboard containers is the amount of paperboard material used. Basically, as a container for foods, the paperboard itself must be of high quality and be food compatible leak proof to a degree, structurally stable, etc. Such material is quite expensive. Thus, any reduction in the blank material required to form the container is highly desirable. As a practical matter, such blanks are normally cut in groups by a single impression or “hit” of the die. In view of the huge numbers of such disposable cartons utilized each year, in the hundreds of millions, any reduction in material, scrap or waste in the forming of the blanks can result in substantial savings and significant economical and ecological advantages.

SUMMARY OF THE INVENTION

The present invention, in an acknowledged extremely crowded art, has several important objects which are considered to advance the art in a patentably significant manner.

Two principal and interrelated objects involve an economically significant reduction in the material used in the formation of the container, and the formation of a container with enhanced heat retention capabilities.

In achieving the above objects, it is also an intention of the present invention to provide a container which presents an attractive contemporary appearance with contoured lines and, as desired, an enhanced surface display area.

Inasmuch as a substantial loss of heat from a received product results from the rather large corner air spaces provided in the conventional or traditional clamshell container, the present invention specifically provides for the reduction of these air spaces by utilizing concave walls as opposed to the more conventional planar or flat walls. Basically, both the tray walls and at least the majority of the lid or cover walls are concavely arced from about the tray bottom and cover top to define an area generally corresponding to that of a circular hamburger bun.

The opposed ends of each tray wall panel arc inwardly and are joined, at corners, appreciably inwardly spaced from a similar corner-forming joinder were the walls panels joined at right angles as in the conventional planar configuration of a traditional clamshell. As an example, in comparison to a conventional container tray of approximately four inches by four inches, an arc from the central section of each wall to each end thereof sufficient to inwardly offset the corner forming end portions ⅛ inch will reduce the length of the side edge of the formed tray a total of ¼ inch. As compared to the traditional clamshell, this in turn will reduce each corner air space, on a radial line bisecting the formed corner, approximately 25%. The reduction in the corner air spaces, while in no way affecting the reception of the hamburger or like foodstuff within the container, will inherently enhance the heat retention capability of the closed container. With similar structural enhancements of the cover of the tray, the length of the opposed sides of each clamshell forming blank can be reduced as much as ½ inch. Such a savings in material, when producing literally millions of such blanks and containers, as noted above, is of tremendous significance both ecologically and economically, particularly when considering the single use disposable nature of the clamshell containers. Thus, it will be recognized that the two principal objects of the invention are achieved, that of substantially reducing the space within the container and the heat loss arising therefrom, and a significant reduction in the material required in the formation of the blank and container, all without affecting the basic function of the clamshell as a means for retaining a common foodstuff.

As will be recognized as the invention is further explained and illustrated, in bringing together the ends of adjoining wall portions to define the reduced air spaces, corner angles of slightly greater than 90° are formed. This will allow minor although significant modifications in the joined ends of the walls which will provide for elimination of additional paperboard material for further savings.

The various objects and advantages residing in the present invention will be better appreciated from the following more detailed description and drawings presented for illustration of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a cross-sectional view of a typical prior art clamshell container with a hamburger sandwich illustrated in phantom lines therein;

FIG. 1B is a similar cross-sectional view taken through the clamshell container of the present invention and illustrating the inwardly shifted corners providing the reduced internal air spaces and enhanced sealing between the tray and lid walls;

FIG. 2A illustrates the prior art blank from which the traditional container of FIG. 1A is folded;

FIG. 2B illustrates the improved blank of the present invention from which the container of FIG. 1B is folded;

FIG. 3 is an enlarged detail view of a typical tray corner area as indicated on FIG. 2B superimposed on a phantom line showing of the corresponding corner area of the prior art container;

FIG. 4 illustrates a nested layout allowed by the blank of the present invention for the simultaneous formation of multiple blanks with a single die impression;

FIG. 5 is a perspective view of the clamshell container of the invention with the lid or cover open; and

FIG. 6 is a perspective view of the closed clamshell container with the rather taller cover front wall presenting a significant display panel.

DESCRIPTION OF PREFERRED EMBODIMENT

Referring now more specifically to the drawings, FIGS. 1A and 2A illustrate the traditional prior art clamshell container includes a tray 10 and a lid or cover 12 integrally joined and folded from a single blank 14. The tray 10, referring both to the folded container and the blank 14, includes a flat rectangular bottom or bottom panel 16 sized to, in the preferred embodiment, receive a hamburger sandwich as suggested in the phantom line showings. Opposed planar tray side panels 18 are integral with opposed side edges of the bottom panel 16 along linear fold lines. Similarly, opposed planar front and rear tray wall panels 20 and 22 are integral with the front and rear edges of the tray bottom along linear fold lines.

The cover 12 is similarly formed with a rectangular top or top panel 24, opposed side walls 26 integral with opposed side edges of the top panel 24 along linear fold lines, and opposed planar front and rear cover walls 28 and 30 also integral with the top panel and foldable relative thereto along linear fold lines. The rear walls 22 and 30 of the tray and cover are integrally joined along a linear hinge forming fold line 32 for a selective opening and closing of the cover. As is traditional, appropriate glue and latch tabs 34 will be used in assembling the container and securing the folded tray and container walls at the respective corners.

Noting the cross sectional detail of FIG. 1A in particular, it will be seen that a traditional container formed from flat panels along straight fold lines, as above described, while capable of receiving and carrying takeout foods, is not particularly effective in retaining heat. This is due both to rather large air spaces 36 provided at the various corner areas of the tray and cover, and in light of the less than effective sealing of the cover walls with the tray walls, resulting in spaces or gaps as suggested at 38.

Referring now to the present invention, attention is directed to FIGS. 1B and 2B, and initially to the blank 39 illustrated in FIG. 2B. As with the prior art blank 14, the blank 39 includes both a tray 40 and a cover 42. While the blank 39 also includes all of the basic components of the prior art blank 14, including top and bottom panels, peripheral walls, glue flaps, and the like, significant differences exist with regard to the structure and relationship of the components to each other.

More particularly, the opposed side walls 44 of the tray 40 are integral with the opposed side edges of the tray bottom 46 along arcuate fold lines 48 which are convex relative to the tray bottom 46. The fold lines 48 each include opposed end portions 50 distinctly inwardly offset relative to the central section or center point 52 of the corresponding fold line 48. It will be appreciated that the maximum transverse width of the tray bottom 46 will be between the central points 52 of the opposed side walls fold lines 48. As suggested by the phantom line showing of the hamburger, this transverse width will be essentially equal to the transverse width of the prior art carton or container. However, as will be noted and as is particularly significant, the transverse width between aligned and opposed end portions 50 of the two fold lines 48 will be appreciably reduced while at the same time in no way interfering with the space required for the accommodation of the hamburger.

The front and rear walls 52 and 54 of the tray 44 are similarly foldably joined to the front and rear edges of the tray bottom 46 along arcuate fold lines 56. The fold lines 56, as with the fold lines 48, have the opposed and aligned end portions 58 thereof inwardly offset with the transverse distance between the front and rear fold lines 56 being at a maximum spacing at the center points and at a minimum spacing at the fold line end portions 58.

The adjoining end portions of the fold lines 48 and 56 and the associated wall panels define the four corners 60 of the tray 40. The corners 60 formed by the joined wall panel ends are inwardly offset and defining an obtuse angles, that is an angle greater than 90°, as opposed to the right angle corners 62 formed by the joined panel ends of the conventional carton tray 10. In this regard, note the enlarged detail of FIG. 3 and the overlay relationship shown therein for purposes of illustration. The space 64 between the fold lines of the conventional tray and the inwardly offset end portions 50 and 58 of fold lines 48 and 56 represents a reduction in the material required in the formation of the blank 39 which is substantial. For example, in a container tray of conventional size, approximately 4 inches by 4 inches, a ⅛ inch radius arc from the center point of each fold line to each corner, that is an arc which will inwardly offset each corner of each fold line ⅛ inch from the center point thereof, will result in a space saving and reduction of material equal to ⅛ inch for a total of ¼ inch in the edge dimension of the tray both along the sides and across the front and rear thereof. In addition to the significant material reduction, it will also be noted that by in effect inwardly offsetting the corners, the corner spaces about the hamburger are also reduced. Using the ⅛ inch reduction noted above, this space reduction will produce a reduction of approximately 25% between the new corner position and the received hamburger. Note the dimension line 66 in FIGS. 2B and 3. Incidentally, in addition to the savings in material uniquely produced by the inward offsetting of the corner construction, and noting the detail of FIG. 3 in particular, additional material reduction, as suggested at 68, will also occur at the ends of the wall panels and the interposed glue flaps and latching lugs which will be defined to accommodate the repositioned corners.

Referring now more specifically to the container cover 42, and noting in particular the blank 39, as in the conventional container, the cover includes a top or top panel 70, opposed side walls 72, a front wall 74 and a rear wall 76. The cover top 70 has opposed side edges defined by convex fold lines 78 with end portions 80 inwardly offset from corresponding center points 82. The side walls 72 are integral with and fold relative to the top 70 along these fold lines 78. A similar convex fold line 84, with end portions 86 inwardly offset from corresponding center point 88 define the forward edge of the top 70 for a folding of the cover front wall 74. The rear wall 76 of the cover is folded relative to the rear edge of the top 70 along a linear or straight fold line 90. A similar straight fold line 92 is formed between the joined outer edges of the tray and cover rear walls 54 and 76 to define a hinge therebetween. The use of such straight fold lines at these particular fold points is desired to prevent a buckling action as the clamshell container is closed.

It is intended that the dimensional reduction in length and width of the cover 42, and hence the material saving, closely correspond to that previously described with regard to the tray portion 40 of the container. As such, and in order to accommodate the straight rear wall fold line 90, the radii of the side wall and front wall fold lines 78 and 84, and the inward offset of the end portions thereof from the corresponding center points may slightly differ from those of the tray side and rear wall fold lines 48 and 56. Thus, referring to the example of dimensions referred to above, a similar reduction in the cover edge length of approximately ¼ inch will result in a total blank edge length reduction of ½ inch, a very appreciable savings in material when considering the millions of such blanks produced yearly. It will also be recognized that the inward offsetting of the edge portions of the cover fold lines 78 and 84 will, in the closed container, similarly and effectively reduce the cold air space at the interior corners of the closed container.

As is the case with regard to the tray 40, in the cover 42, the transverse distances between the two sets of the generally parallel fold lines is greatest at the center points thereof with the transverse distances reduced at the aligned corner portions. In accommodating the straight rear edge fold line 90 of the top 70 while maintaining the desired edge length reductions as previously noted, this can be achieved by utilizing a shorter radius in defining the side wall fold lines 78 and a greater radius in defining the front wall fold line 84 as compared to the radii utilized for the fold lines 48 and 56 of the tray 40.

Referring again to the tray portion of the blank in FIG. 2B, the tray side walls 44 are preferably formed with arced or convex outer edges and extend, in the closed carton as suggested in FIG. 1B, higher within the corresponding cover side walls 72. The outer edge of each cover side wall 72 is defined by a complimentary concave cut reducing the height thereof an amount equal to the corresponding height increase of the tray side walls, thus not conflicting with the overall material reduction desired in the present invention.

Noting FIG. 4 and the partial layout of multiple blanks for utilization of a single die cut, it will be appreciated that the reverse positioning of adjacent blanks and the complementary configurations of the outer edges of the tray and cover side walls allow for a single “hit” or die cut, thus simplifying manufacture and reducing excess or waste material to a minimum.

A similar complementary configuration will be noted in the preferred front walls 52 and 74 of the tray and cover wherein the outer edge of the tray front wall 52 is concave and relatively shorter than the front wall of a conventional clamshell container. At the same time, the front wall 74 of the cover is substantially taller and includes a convex outer edge, the configuration of which corresponds to that of the concave outer edge of the tray front wall 52. This also allows for a single die cut between adjacent blanks in the formation of the blanks.

The formation of the walls as above described is preferred and provides particular advantages over the prior art “flat panel” container. More particularly, the taller front wall 74 of the cover, as noted particularly in FIG. 6, provides, in conjunction with the curvature of the wall itself, an enlarged display area for logos, designs or any appropriate attractive indicia. The extended height of the cover front wall and the curvature thereof in conjunction with the curvature of the tray front wall ensures a positive continuous engagement of the upper edge of the front tray wall 52 against the inner surface of the elongate overhanging cover front wall 74. Such a relationship also occurs between the overlapping side walls of the tray and cover as will be appreciated from the schematic cross sectional view of FIG. 1B wherein the convex upper edges of the tray side walls, initially at the highest center points thereof, engage against the inner surfaces of the cover side walls with the continuing closing movement of the cover causing a slight inward flexing of the tray side walls until full engagement of the tray side wall upper edges with the inner surfaces of the cover side walls is achieved and the appropriate latching means engaged. This avoids and eliminates the air gap normally experienced in flat-wall containers of the conventional type as illustrated in FIG. 1A. In addition, in utilizing this relationship, it has been found that the cover 44 will actually seat lower on the tray, eliminating unnecessary interior air space and avoiding the undesirable cooling effect thereof.

It will also be appreciated that the finished container itself, particularly when closed as illustrated in FIG. 6 presents an attractive appearance derived from the smoothly curving or arcing contours as viewed from both the front and sides, providing a distinctive appearance desirable for product and/or provider identification.

The foregoing describes a preferred embodiment of the invention and is considered illustrative of the principles of the invention. In the description above, the front wall of the container is described as being concave and the front wall of the cover as convex. If desired, and still within the scope of the invention, these shapes could be reversed or even have a straight line cut. It is to be understood that as modifications and changes may occur to those skilled in the art, it is not desired to limit the invention to the exact construction as shown and described. Rather, all suitable modifications and equivalents may be resorted to as falling within the spirit and scope of the invention as set forth in the appended claims. 

1. A clamshell container of foldable paperboard particularly adapted for reception of a heated foodstuff, said container being configured for reduced utilization of paperboard and enhanced retention of heat, said container comprising a tray and a cover, each of generally rectangular configuration, said tray having a bottom with opposed side edges and opposed front and rear edges, said tray further including opposed laterally spaced front and rear walls folded upwardly respectively from said front and rear edges of said tray bottom, the laterally spaced relation between said front and rear walls being at a maximum at aligned opposed central sections of said front and rear walls, said front and rear walls having opposed end sections inwardly of the respective central sections and defining, relative to the space between the central sections, a reduced spacing between aligned and opposed respective end sections of said front and rear walls for close accommodation of said front and rear walls to a received foodstuff, said tray further including opposed laterally spaced side walls folded upward respectively from said opposed side edges of said tray bottom, the laterally spaced relation between said side walls being at a maximum at opposed central sections of said side walls, said side walls each having opposed end sections inward of the respective central sections and defining a reduced spacing at opposed respective end sections of said side walls for close accommodation of the side walls to a received foodstuff, said side walls at opposed ends thereof, joining to and forming corners with corresponding ends of said front and rear walls to define corners inwardly offset relative to said maximum spaced central sections and restricted corner air spaces within said tray for minimizing heat loss from a received heated foodstuff.
 2. The clamshell carton of claim 1 wherein said tray walls each follow a constant arc along the corresponding edge of the tray bottom.
 3. The clamshell container of claim 2 wherein said front, rear and side walls have upper edges and incline outward from said bottom to said upper edges.
 4. The clamshell container of claim 3 wherein the edges of the tray bottom are defined by convex fold lines about which the walls fold upwardly and which define the arcs of the walls.
 5. The clamshell container of claim 4 wherein said front and side walls maintain said constant arc from said tray bottom to the upper edges thereof, the arc of said rear wall at the corresponding edge of the tray bottom progressively decreasing upward from said tray bottom to the upper edge of said rear wall.
 6. The clamshell container of claim 5 wherein said container cover includes a cover top defined by laterally spaced opposed side edges and laterally spaced opposed front and rear edges, opposed laterally spaced cover side walls folded from said top side edges, and opposed laterally spaced front and rear cover walls folded from said front and rear edges of said cover top, said front edge and said side edges of said cover top each being defined by a convex fold line about which the corresponding walls fold, said cover side and front walls being convex relative to said cover top with the arc of each of these walls being defined by the corresponding fold line between the wall and the top.
 7. The clamshell container of claim 6 wherein said rear edge of said cover top is defined by a straight fold line, said cover rear wall being planar.
 8. The clamshell container of claim 7 wherein said tray rear wall and said cover rear wall have common outer edges joined along a straight fold line providing hinge means between said cover and said tray for a selective closing of said cover over said tray.
 9. The clamshell container of claim 8 wherein, upon a closing of said cover over said tray, said cover side and front walls overlie said tray side and front walls in intimate contact with the upper edges of said tray side and front walls, said cover front wall being of a substantially greater height than said tray front wall.
 10. A clamshell container formed of foldable paperboard and comprising a tray and a cover, said tray comprising a bottom panel with opposed side edges and opposed front and rear edges, a pair of transversely spaced side walls integral with and folded from said opposed side edges of said bottom panel along convex side fold lines, each side fold line defining an arcuate configuration to the corresponding side wall above said bottom panel, said tray further including transversely spaced front and rear walls respectively integral with and folded from the opposed front and rear edges of said bottom panel along a convex front fold line and a convex rear fold line, said front and rear fold lines defining an arcuate configuration to each of said front and rear walls above said bottom panel, said cover comprising a top panel, said top panel having opposed side edges and opposed front and rear edges, a pair of opposed transversely spaced cover side walls and a cover front wall integral with and folded from corresponding side and front edges of said top panel along fold lines convex relative to said top panel, and a cover rear wall opposed to and transversely spaced from said cover front wall, said cover rear wall being integral with and folded from a linear fold line defining said rear edge of said top panel, said tray rear wall and said cover rear wall having a common outer edge defined by a linear fold line forming a hinge joinder between said tray and said cover for selective closing of said cover over said tray.
 11. The clamshell container of claim 10 wherein the transverse spacing between the walls of each pair of opposed walls of both the tray and the cover is at a maximum at the central point of each wall with this transverse spacing decreasing between each pair of opposed walls toward opposite ends of the walls of each pair of opposed walls, whereby the transverse spacing between corresponding ends of each pair of opposed walls is less than the transverse spacing between the corresponding center points of the same pair of opposed walls.
 12. The clamshell container of claim 11 wherein the ends of each tray wall are joined to adjacent ends of adjoining walls to form four corners about said tray bottom, each corner defining an included angle of greater than 90°.
 13. A container blank foldable to define a tray and cover, said blank including a tray section and an aligned cover section, said tray section having a central bottom panel defined by a pair of opposed convex side wall fold lines, a convex front wall fold line and an opposed convex rear wall fold line, a pair of opposed side wall panels integral with said bottom panel and foldable relative thereto along said side wall fold lines, a front wall panel and a rear wall panel integral with said bottom panel and foldable relative thereto respectively along said front and rear wall fold lines, each convex wall fold line being at a transverse spacing from the opposed fold line which is at a maximum at transversely aligned center points of the opposed fold lines and which progressively decrease outward from the central points to a minimum spacing at transversely aligned ends of the opposed fold lines.
 14. The blank of claim 13 wherein said cover section has a central top panel defined by a pair of opposed convex side wall fold lines, a front wall fold line and an opposed rear wall fold line, a pair of opposed cover side wall panels integral with said top panel and foldable relative thereto along said top panel side wall fold lines, a cover front wall panel and a cover rear wall panel integral with said top panel and foldable relative thereto respectively along the front and rear top panel fold lines.
 15. The blank of claim 14 wherein said top panel front wall fold line is convex.
 16. The blank of claim 15 wherein said cover rear wall fold line is linear, each cover convex wall fold line being at a transverse spacing from the opposed fold line which is at a maximum at transversely aligned center points of the opposed fold lines and which progressively decrease outward from the center points to a minimum spacing at transversely aligned ends of the opposed fold lines.
 17. The blank of claim 16 wherein said rear wall panels of said tray section and said cover section have a common linear outer edge defined by a hinge-forming linear fold line.
 18. The blank of claim 17 wherein said tray front wall panel has a concave arc outer edge, said cover front wall panel having a convex arc outer edge complementing the concave arc of the tray front wall panel outer edge.
 19. The blank of claim 18 wherein the cover front wall is of a transverse width greater than that of the tray front wall panel to define an enhanced display surface in a folded container.
 20. The blank of claim 19 wherein said tray side wall panels have arced outer edges, said cover side walls panels having arced outer edges complementing the arcs in the outer edges of the tray side wall panels for a simultaneous defining of these outer edges between duplicate blanks when simultaneously cutting multiple blanks. 